Cold isostatic pressing
Isostatic pressing is cold isostatic pressing. According to the different forming process, it can be divided into two forms: wet bag type and dry bag type. Wet bag isostatic pressing technology is to put granulated ceramic powder or pre-formed billet into the deformable rubber envelope, and then apply uniform pressure through the liquid, when the pressing process is over, and then the rubber envelope with billet body out of the container, this is a discontinuous forming method.
The advantages of this technology are relatively low cost, the flexibility of forming products of different shapes, and the pressure can reach 500MPa. This technology can be used in laboratory and certain scale production, and can be molded parts of medium complexity, its disadvantage is that the number of molded products in a certain time is small. The technique of drybagisostaticpressing is to fill ceramic powder in batch into flexible preforming die and then apply isostaticpressing. Since the mold is fixed in the equipment, the molded product is pushed out when the pressing is finished. Figure 3-9 shows the principle of dry bag isostatic pressing. "Dry bag" molding cycle is short, mold service life is long, especially convenient for large-scale continuous chemical industry production. The mold material is polyurethane synthetic rubber or silicone rubber. Compared with wet bag type isostatic pressing molding, dry isostatic pressure is low, generally within 200 MPa. The most familiar ceramic spark plug is currently formed by dry bag type isostatic pressing, pressing time is usually only 1~2 s.
Isostatic molding has the following advantages over steel molding:
① Can be formed with concave, hollow slender parts and other complex shapes of the parts
Small friction loss, forming pressure
③ The pressure is transferred from all aspects, and the density distribution of the billet is uniform and the strength of the billet is high
The mold cost is low.
The disadvantages of wet isostatic pressing are: the size and shape of the blank is not easy to control accurately, the production efficiency is low, and the automation is not easy. The dry bag isostatic pressing method can overcome these disadvantages to some extent.
1. Defects and control of isostatic pressing
It mainly includes:
(1) The neck formed by uneven filling, which is related to the poor fluidity of powder;
(2) Irregular surface caused by uneven powder filling or unsupported rubber bag loading;
(3) In wet isostatic pressure, the "image foot" shape is formed because the rubber bag of the mold is too hard or because the compressibility of the powder is too large;
(4) The "banana" shape formed by the rubber mold bag without support in wet isostatic pressure;
(5) compression cracks formed by axial elastic rebound in forming, especially for hard powder;
(6) The formation of delamination due to compression cracks, which comes from inappropriate or too thick rubber materials or weak billets;
(7) irregular surface shape, and the sealing rubber bag material is not suitable or too thick, the strength of the blank body is low or small angular radius;
(8) Axial cracks formed due to insufficient elasticity.
2. The application of cold isostatic pressing technology
Because cold isostatic pressing technology can improve product performance. Improve product quality, increase economic benefits, compared with other molding processes, there are many attractive advantages, therefore, the application field is expanding, the technology is becoming more and more mature. So far, the isostatic pressure technology has been used in hundreds of product categories.
Jiangsu High Industry focuses on the research and production of isostatic pressing moulds, customizes various dry bag and cold isostatic pressing moulds, adapts to different models of various manufacturers at home and abroad, and deeply understands the needs of various industries. Alloy, graphite and other industries provide high-performance isostatic pressing mold rubber sleeves.
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